两种完熟相关基因反义RNA在转因番茄中的表达及其对果实完熟的仰制作用

植物激素乙烯作为一种信使分子调节控制果实完熟。ACC合成酶是植物体内乙烯生物合成途径的限速酶，其反义RNA的表达将能有效地抑制乙烯的生物合成而延缓果实完熟，利用反转录PCR技术克隆获得了ACC合成酶多基因家族成员之一LE-ACC2阅读框架约1.7kb的cDNA，经酶切图谱和序列分析鉴定无误后，反向连入植物表达载体pBin437中构建成组成型表达ACC合成酶反义RNA的双元载体。经农杆菌途径转化番茄“丽春”品种，获得了60株抗卡那再生杭株，PCR检测证明有6株为转基因植株，Southern杂交和Northern杂交分析进一步确证了外源基因的插入及其转录活性。反义番茄果实的乙烯释放受到明显抑制，表现出更好的耐储保鲜特性，并且与对照相比，在果实品质上没有明显差别。大田培育Fl和F2代转化番茄植株，反义番茄纯合品系的筛选工作正在进行之中。 同时，本研究利用已经获得的ACC合成酶和PG的cDNA克隆，构建了两个嵌合转化基因载体pPGACC1、pPGACC10，它包括1300bp的ACC合成酶cDNA编码序列，并分别含有反向与正向的250bp的5’端PG基因片断。酶切图谱和序列分析鉴定无误后，以pBin437为植物表达载体构建了双元载体pBPGACC1和pBPGACC10，分别表达PG正义RNA和反义RNA，并均表达ACC合成酶反义RNA。经农杆菌转化番茄子叶，植株的再生培育有待进行。通过对转基因植物的分析，我们期望阐明用单一嵌合基因表达载体通过反义抑制与抑制作用实现对内源两同源基因——PG和ACC合成酶下降调节的可能性，并可望得到具有更好耐储效果且品质优良的番茄品系。

小麦杂交坏死蛋白质组学研究

小麦杂交坏死是某些小麦杂交种表现出的叶片提前逐渐死亡的现象。它是由两个坏死基因Ne1和Ne2在杂交种中相遇后发生显性互补引起的。坏死从叶片尖端逐渐过渡到叶片基部，从成熟叶片发展到幼嫩叶片。一些严重坏死的F1完成它的生活周期前就在不同的生长阶段死去，无法获得F1种子，这就限制了携带优良性状的亲本的选择和优良基因的交流。另外，小麦杂交坏死是一个独特的研究植物程序性死亡的遗传系统。虽然小麦杂交坏死这种现象已经发现很多年，但其详细的分子机理却仍然未知。对小麦杂交坏死的分子机理进行深入研究将有助于克服小麦杂交利用中杂交坏死的遗传障碍，此外，也为深入研究植物的PCD机理提供可操作靶分子。 本论文采用高通量蛋白质组研究技术对小麦杂交坏死进行了研究。携带坏死基因Ne2的小麦品种Pan555（P）和携带坏死基因Ne2的小麦品种Zheng891（Z）生长发育完全正常，将两个亲本杂交，所得杂交F1代PZF1表现杂交坏死。在小麦生长阶段8，旗叶（Flag leaf）刚刚出现，PZF1的旗叶下第一片叶子（FL-1）还是完全绿色，FL-2叶尖开始有坏死斑出现。在这个阶段，分别将PZF1，P，Z的FL-2叶剪成相等的尖，中，基三段。我们选择的PZF1的FL-2叶，其叶尖段已经有成片的坏死斑出现;中间段零星出现少量坏死斑点;基部段和亲本一样还是完全的绿色，代表坏死进程中的不同阶段。又选PZF1的FL-1和FL-2分别代表杂交坏死启动前和杂交坏死启动后。两个亲本P和Z的FL-2叶的三段及FL-1叶正常，都是完全绿色。 首先分别分析了PZF1，P和Z的FL-2叶的尖、中、基三段的蛋白表达情况。在PZF1的尖、中、基三段共检测到23个差异表达蛋白点。这23个点在两个亲本的尖、中、基三段中的表达丰度没有显著差异（p<0.05），说明这23个蛋白的差异表达不是由于叶段的不同引起，确与杂交坏死相关。对这23个蛋白进行了MALDI-TOF质谱鉴定，其中18个得到成功鉴定。然后对PZF1，P和Z的FL-1叶和FL-2叶的蛋白表达情况进行了分析。与PZF1的FL-1叶比较，在FL-2叶中检测到19个蛋白上调，20个蛋白下调。这39个蛋白的丰度在两个亲本的FL-1和FL-2叶之间没有显著差异，说明这39个蛋白的差异表达不是由于叶位的不同引起，确与杂交坏死相关。对这39个蛋白进行质谱鉴定其中26个得到成功鉴定。 根据被鉴定蛋白的功能及其表达丰度的变化，对这些蛋白在小麦杂交坏死中可能的作用进行了讨论。与PZF1的FL-2叶基部相比，S-腺苷同型半胱氨酸水解酶（S-adenosyl homocysteine hydrolase）在中部极显著（p<0.01）下调，而在中部和尖段之间没有显著差异，保持低丰度不变。腺苷甲硫氨酸3（AdoMet synthase 3）和甲硫氨酸合成酶1（Methionine synthase 1）都在PZF1的FL-2叶尖段上调。甲基化循环中的这3个酶比例的不协调可能会以不同的方式加速细胞老化。 与PZF1的FL-1叶比较，尿卟啉环脱羧酶（Uroporphyrinogen decarboxylase）在FL-2叶中下调，这将引起尿卟啉环III的积累。脂加氧酶（Lipoxygenases）在FL-2叶中上调。尿卟啉环III的积累和脂加氧酶的上调都会引起细胞内活性氧的增加。另外活性氧和脂加氧酶都会使脂发生过氧化作用，进而导致细胞膜完整性受到破坏，最终可能导致细胞死亡。 与基部段比较，在PZF1的FL-2叶的尖段和/或中间段;以及与PZF1的FL-1叶比较，在FL-2叶中，都有很多防御性蛋白的上调，这暗示应对活性氧、脂过氧化、甲基化循环中三个酶比例的不协调等引起的对细胞的破坏作用，细胞可能启动了抗细胞死亡系统来应对这种细胞内部的胁迫。 然而，与基部段比较，一些能量相关蛋白在PZF1的FL-2叶的尖段和/或中间段;以及与PZF1的FL-1叶比较，在FL-2叶中的异常表达可能会以干扰能量循环的方式加速细胞死亡。另外，与FL-2基部段比较，在尖段和/或中间段，以及与PZF1的FL-1比较，在FL-2中，都有一些防御性蛋白、蛋白合成相关的蛋白以及单链DNA结合蛋白下调，它们的变化可能会降低细胞的抵抗力，蛋白合成能力以及DNA修复能力。细胞正常代谢的很多方面都受到干扰从而使PZF1叶细胞最终走向死亡。 本研究中发现了三个甲基化循环中的酶变化，而且S-腺苷同型半胱氨酸水解酶是在坏死进程的较早阶段发生下调，它的变化可能是小麦杂交坏死的一个诱因，这暗示小麦杂交坏死可能是一个表观遗传学事件。另外本研究还发现一些和活性氧，脂氧化等相关的蛋白的变化，而活性氧增加和脂氧化都是细胞凋亡的典型特征。所以本研究为表观遗传细胞凋亡和氧化胁迫细胞凋亡的研究提供了很有价值的信息。

一氧化氮在磷酸盐调节拟南芥根系形态变化中的作用

磷缺乏已成为制约世界农业生产的重要因子。植物根系的大小和形态是决定植物吸收土壤磷能力的重要因素，而且根系的生长发育与磷素的分布及其有效性密切相关。关于磷酸盐调节植物根系生长研究已有很多报道，但其生理和分子机制仍不清楚。一氧化氮 (NO) 是一种重要的气体信号分子，参与调控植物的生长发育和对多种逆境胁迫的应答反应。本文选用拟南芥为实验材料，研究探讨了NO与缺磷诱导的拟南芥根系形态变化之间的关系，主要结果如下： 用正常磷水平 (1 mM) 和低磷水平 (1 µM) 处理拟南芥幼苗，发现低磷抑制主根伸长，刺激侧根发生。外源NO供体销普纳 (SNP) 也抑制主根、刺激侧根生长，与低磷诱导根系形态变化相似。NO清除剂c-PTIO和一氧化氮合成酶 （NOS）抑制剂L-NNA均可部分减缓由低磷引起的对主根生长的抑制和对侧根的刺激作用。暗示低磷诱导的拟南芥根系形态的变化可能与NO含量的降低有关。 利用NO荧光标记物DAF-FM和激光共聚焦显微成像技术，本研究发现缺磷6 h和24 h后根细胞内源NO含量显著增加，而且NOS 抑制剂能减少低磷诱导的根细胞NO含量的增加。与正常供磷处理相比，低磷处理6 h和24 h，拟南芥根中编码与NO合成相关的基因（AtNOA1）的表达量增加，缺磷24 h后根中NOS酶活性升高。为了明确低磷诱导的NO 增加是否与硝酸还原酶（NR）介导的NO合成有关，本论文进一步研究了低磷对拟南芥硝酸还原酶活性和编码NR基因 （AtNR1和AtNR2）表达的影响。研究发现低磷处理6 h和24 h后和AtNR1和AtNR2基因的表达均没有变化，且蛭石中生长的拟南芥缺磷1个月后NR活性也没有发生变化;拟南芥的NR双突变体nia1，nia2在低磷处理24 h后，其根中的内源NO含量表现出与野生型相同的增加。因此这些研究结果表明，缺磷后拟南芥根细胞NO的含量增加主要由于NOS的活性升高，而与NR介导的NO合成无关。 已有资料表明低磷诱导植物根细胞内源过氧化氢（H2O2）分布和含量的变化。本论文研究了低磷处理对用H2O2标记物CM-H2DCFDA标记不同磷处理下的拟南芥根中的H2O2。研究发现，缺磷6 h根中H2O2的分布无明显变化，缺磷24 h后H2O2呈斑块状分布，且多集中在根尖伸长区。缺磷24 h后，叶片中的抗氧化保护酶—超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性没有明显变化。说明缺磷24 h 后产生的H2O2没有引起氧化胁迫，而是作为一种信号分子，与NO相互作用共同介导低磷胁迫的应答反应。关于NO与H2O2在低磷诱导的根形态变化中的信号转导过程还有待进一步研究。

中国淋巴囊肿病毒胸苷酸合酶基因结构特点及分析

胸苷酸合酶(Thymidylate synthase, TS)是进行 DNA 合成所必需的酶类,与细胞分化及肿瘤发生密切相关。淋巴囊肿病毒属于虹彩病毒科成员,是能引起百余种淡、海水鱼感染,并产生肿瘤的病毒病原。在已完成中国淋巴囊肿病毒株 (Lymphocystis disease virus-China, LCDV-C) 基因组序列测定的基础上,本文对位于 LCDV-C 基因组开放阅读框 ORF 011L 的 TS 基因结构、及其推定蛋白结构进行了分析。该基因全长 858bp,GC 含量为 28.2%,编

Effects of tetrabrominated diphenyl ether and hexabromocyclododecanes in single and complex exposure to hepatoma HepG2 cells

This study was designed to determine cytotoxic effects of PBDE-47 and HBCDs individually or with a mixture of both compounds exposure to Hep G2 cells. The results showed PBDE-47 and HBCDs induced increase of nitric oxide synthase (NOS) activity, release of NO. dissipation of mitochondria membrane potential and cell apoptosis. Exposure to HBCDs induced ROS formation. Moreover, preincubation with PTIO (NO scavanger) and N-acetylcysteine (ROS scavanger) partially reversed cytotoxic effects of these compounds. The possible mechanism is that PBDE-47 and HBCDs could boost generation of NO and/or ROS, impact mitochondria, and result in start-ups of apoptosis program. Cells exposed to mixture of both compounds and each of them showed non-apoptotic rate significant difference, but the combination of them caused more adverse effects on cells. These results Suggest that PBDE-47 and HBCDs in single and complex exposure have the cytotoxic activity of anti-proliferation and induction of apoptosis in tumor cells in vitro. (C) 2008 Elsevier B.V. All rights reserved.

UV-B-induced Oxidative Damage and Protective Role of Exopolysaccharides in Desert Cyanobacterium Microcoleus vaginatus

UV-B-induced oxidative damage and the protective effect of exopolysaccharides (EPS) in Microcoleus vaginatus, a cyanobacterium isolated from desert crust, were investigated. After being irradiated with UV-B radiation, photosynthetic activity (Fv/Fm), cellular total carbohydrates, EPS and sucrose production of irradiated cells decreased, while reducing sugars, reactive oxygen species (ROS) generation, malondialdehyde (MDA) production and DNA strand breaks increased significantly. However, when pretreated with 100 mg/L exogenous EPS, EPS production in the culture medium of UV-B stressed cells decreased significantly; Fv/Fm, cellular total carbohydrates, reducing sugars and sucrose synthase (SS) activity of irradiated cells increased significantly, while ROS generation, MDA production and DNA strand breaks of irradiated cells decreased significantly. The results suggested that EPS exhibited a significant protective effect on DNA strand breaks and lipid peroxidation by effectively eliminating ROS induced by UV-B radiation in M. vaginatus.

Effects of hexachlorobenzene on antioxidant status of liver and brain of common carp (Cyprinus carpio)

Hexachlorobenzene (HCB)-induced oxidative damages have been published in rats while the effects have not yet been reported in fishes. Juvenile common carps (Cyprinus carpio) were exposed to waterborne HCB from 2 to 200 mu g l(-1) for 5, 10 or 20 days. Liver and brain were analyzed for various parameters of oxidative stress. There were no significant changes of glutathione (GSH) content and superoxide dismutase (SOD) activity in liver after 5 or 10 days exposure, whereas obvious drops were observed at higher concentrations after 20 days exposure. Significant decreases of GSH content and SOD activity in brain were found during all the exposure days. In brain, HCB also significantly elevated the contents of reactive oxygen species (ROS), thiobarbituric acid-reactive substances (TBARS, as an indicator of lipid peroxidation products), glutathione disulfide (GSSG), and activities of nitric oxide synthase (NOS), glutathione peroxidase (GPx), and glutathione reductase (GR), and inhibited activities of acetylcholinesterase (AchE) and glutathione S-transferase (GST). The results clearly demonstrated that environmentally possible level of HCB could result in oxidative stress in fish and brain was a sensitive target organ of HCB toxicity. (c) 2006 Elsevier Ltd. All rights reserved.

Effects of salt stress on carbohydrate metabolism in desert soil alga Microcoleus vaginatus Gom.

The effects of salt stress on carbohydrate metabolism in Microcoleus vaginatus Gom., a cyanobacterium isolated from desert algal crusts, were investigated in the present study. Extracellular total carbohydrates and exopolysaccharides (EPS) in the culture medium produced by M. vaginatus increased significantly during the growth phase and reached a maximum during the stationary phase. The production of extracellular carbohydrates also significantly increased under higher salt concentrations, which was attributed to an increase in low molecular weight carbohydrates. In the presence of NaCl, the production of cellular total carbohydrates decreased and photosynthetic activity was impaired, whereas cellular reducing sugars, water-soluble sugars and sucrose content and sucrose phosphate synthase activity increased, reaching a maximum in the presence of 200 mmol/L NaCl. These parameters were restored to original levels when the algae were transferred to a non-saline medium. Sodium and K+ concentrations of stressed cells decreased significantly and H+-ATPase activity increased after the addition of exogenous sucrose or EPS. The results suggest that EPS and sucrose are synthesized to maintain the cellular osmotic equilibrium between the intra- and extracellular environment, thus protecting algal cells from osmotic damage, which was attributed to the selective exclusion of cellular Na+ and K+ by H+-ATPase.

Salt tolerance of Microcoleus vaginatus Gom., a cyanobacterium isolated from desert algal crust, was enhanced by exogenous carbohydrates

Microcoleus vaginatus isolated from a desert algal crust of Shapotou was cultured in BG-11 medium containing 0.2mol l(-1) NaCl or 0.2mol l(-1) NaCl plus 100mg l(-1) sucrose, extracellular polymeric substances (EPS) or hot water-soluble polysaccharides (HWP), respectively. Photosynthetic oxygen evolution rates, photosystem 11 activity (Fv/Fm) and dark respiration of NaCl-stressed cells were enhanced significantly by the added sucrose or EPS under salt stress conditions (0.2mol l(-1) NaCl). Compared with cells treated with salt alone, sodium contents in cells reduced significantly; the content of cellular total carbohydrate did not change, and intracellular sucrose, water-soluble sugar increased significantly following the addition of exogenous carbohydrates. Sucrose synthase (SS) activity of NaCl-stressed cells increased following the addition of sucrose, and sucrose phosphate synthase (SPS) activity of NaCl-stressed cells increased following the addition of exogenous sucrose, EPS or HWP compared with cells stressed with NaCl only. The results suggested that the extruded EPS might be re-absorbed by cells of M. vaginatus as carbon source, they could increase salt tolerance of M. vaginatus through the changes of carbohydrate metabolism and the selective uptake of sodium ions. (C) 2003 Elsevier Science Ltd. All rights reserved.

RNAi沉默烟草GA 20-氧化酶基因研究

赤霉素是一种高效能的广谱植物生长调节剂，为五大植物激素之一，具有重要的生物学功能。目前利用赤霉素突变体研究生物合成途径和信号转导已经成为热点。 GA 20-氧化酶是GA生物合成中的一类关键酶，它位于GA合成途径的中心位置。本研究根据烟草（Nicotiana tabacum）GA 20-氧化酶基因序列，设计2对分别含有特定酶切位点的特异引物，以烟草基因组DNA为模板，扩增目的基因(约250 bp)片段。将正、反向目的片段分别插入中间载体的内含子两侧，再经BamH I和Sac I双酶切回收约700 bp的目的片段，插入到双元载体质粒p2355中，成功构建了含GA 20-氧化酶基因片段反向重复序列的植物表达载体p23700。分别将p2355质粒和p23700质粒导入根癌农杆菌（Agrobacterium tumefaciens）EHA105中并转化烟草叶片细胞，经卡那霉素选择培养，PCR及GUS组织染色鉴定，获得转基因烟草植株。以EHA105-p2355转化的烟草，获得41株转基因植株，均没有矮化表型；而以EHA105-p23700转化的烟草，获得转基因植株14株，其中具有矮化表型的烟草10株，表明反向重复序列转录产物能形成发夹RNA(hpRNA)，产生小分子干扰RNA（small interferring RNA，简称siRNA），干扰目的基因的表达。 赤霉素含量测定表明矮化植株中赤霉素合成途径的最终产物GA3总含量明显低于野生型烟草植株。荧光定量PCR结果表明，矮化转基因烟草的GA 20-氧化酶基因表达量受到明显抑制，表达量明显低于野生型对照。同时对上游内根-贝壳杉合成酶（Ent-kaurene synthase，KS）基因，下游的GA-3β羟化酶基因进行了RT-PCR分析，结果显示上游基因的表达没有规律性变化，而下游基因表达量亦降低。上述结果表明，GA 20-氧化酶基因的表达被有效地干扰了，表达受到抑制，从而影响植株体内GA3的合成，影响植株的生长发育，导致植株矮化。并推测，GA 20-氧化酶基因受到抑制，可能影响下游基因的表达。并且通过干旱胁迫测试，发现矮化植株相对于野生型植株及不含干扰片段的转基因植株，对干旱的耐受力有了很大的提高，具有更强的耐受力。 研究结果为进一步进行相关研究奠定基础。 Gibberellin(GA) is an efficient plant growth regulator. As one of five major plant hormones, it plays an important biological function. Using GA mutant for investigating biosynthetic pathways and signal transduction has become high lights. GA 20-oxidase is a crucial enzyme involved in gibberellin biosynthesis. According to tobacco (Nicotiana tabacum) GA 20-oxidase enzyme gene sequence and based on binary vector p2355, we constructed a plant expression vector p23700, which habors an inverted repeat DNA fragment of GA 20-oxidase gene drivered by Cauliflower mosaic virus promtor (CaMV 35Sp). Binary plasmid p2355 had no inverted repeat DNA fragment of GA 20-oxidase gene. The vector p2355 and p23700 were introduced into Agrobacterium tumefaciens EHA105 and tobacco leaf transformation was conducted. After selected by kanamycin and characterized by PCR and GUS hischemical reaction, transsgenic plants were obtained. Fourtheen transgenic plants, which were transformed by EHA105-p23700, were obtained. Among them, 10 were dwarf mutants. However, 41 transgenic plants with the same normal phenotype as wild type,which were transformed by EHA105-p2355, were obtained. Analysis of Gibberellin contents showed that it was lower in dwarf mutants than in normal phenotype plants. Moreover, comparing to normal phenotype plants including wild type and transgenic plants with no interference fragment, the drought tolerance of dwarf plants have greatly increased. And their proline content increased obviously after drought test. Fluorescence quantitative real time PCR (RT-PCR) showed that GA 20-oxidase gene expression was significantly inhibited in dwarf transgenic tobacco. Meanwhile, the expression of the upstream gene ent-kaurene synthase (KS) gene and downstream gene GA-3β hydroxylase gene was also detected by RT-PCR. The results presented that KS gene expression had no regular change while GA-3β hydroxylase gene expression reduced. It implied that inhibiting GA 20-oxidase gene probably reduce the expression of downstream genes. The results showed that the transcriptional products of the foreign inverted repeat fragment can form hairpin RNA (hpRNA) to induce RNAi. It presented that GA 20-oxidase gene expression was effectively interfered, resulting in reducing GA3 synthesis and inhibiting plant growth and development, then dwarf plants were produced. However, the dwarf plants had higher tolerance of drought.

辐射诱导的HeLa细胞旁效应信号通路研究

随着肿瘤认识的不断深入，肿瘤外科学、肿瘤放射治疗学、肿瘤化学治疗学构成了现代肿瘤治疗学的三大支柱，而放射治疗学的研究对于肿瘤的治疗有重要的临床意义。本文通过对HeLa进行辐射来观察其产生的旁效应信号通路，从而对临床工作的起到一定的帮助。辐照过的细胞通过释放信号分子引起周围未辐照细胞产生一系列的生物学反应的现象，称之为辐射诱导的旁效应。活性氧（Reactive oxygen species, ROS）和一氧化氮（Nitric oxide, NO）是辐射诱导的旁效应信号通路中的两个重要信号分子。本文研究了这两种重要的信号分子在辐射诱导的HeLa细胞旁效应信号通路中的关系。通过微核实验，我们发现X射线以及12C6+ 辐照过的HeLa细胞及其旁观者细胞的微核形成明显增加，而1%的二甲亚砜（Dimethyl sulfoxide，DMSO，ROS清除剂）预处理X射线辐照的细胞则显著抑制了受辐照细胞及其旁观者细胞的微核形成。1 Gy的X射线辐照能够抑制细胞的增殖速率而0.5%和1%的DMSO预处理则能减少X射线的增殖抑制作用，并且DMSO预处理的效果与浓度有关：1%的DMSO比0.5%的DMSO处理更大程度的恢复了受辐照细胞的增殖速率。另一方面，接受条件培养基（Conditioned medium）的旁观者细胞的增殖速率增加，而DMSO预处理产生条件培养基的受辐照细胞则使旁观者细胞的增殖速率降低，且DMSO预处理的效果同样与其浓度相关：浓度越高，条件培养基的刺激生长作用越小。Western blotting和DAF-FM DA荧光探针检测分别显示了辐照过后细胞的诱导型一氧化氮合酶（Inducible nitric oxide synthase, iNOS）和NO水平均升高，而DMSO预处理则降低其水平。因此，我们推测在X射线辐照的HeLa细胞旁效应信号通路当中ROS是NO的上游信号。另外，我们采用培养基转移后立即加DMSO或BMS－345541（IKK/NF-κB抑制剂）的方法研究了旁观者细胞当中的旁效应信号通路。我们发现DMSO和BMS－345541均显著抑制了旁观者细胞的NO水平。因此，在旁观者细胞当中ROS与NF-κB均为NO的上游信号

Electrochemical reactions of cyanocobalamin in acidic media

Electrochemical reactions of cyanocobalamin, CN-Cbl[Co(III)], were studied at glassy carbon electrodes in acidic media by means of cyclic voltammetry and differential pulse polarography. It was found that in pH 0 solution, CN-Cbl[Co(III)] exists mainly in the base-off form, {CN-Cbl[Co(III)]}(base-off). It can undergo a one-electron reduction and a follow-up chemical reaction to form {H2O-Cbl[Co(II)]}(base-off). The rate-constant k of the follow-up decyanation reaction is 0.022 s(-1). {H2O-Cbl[Co(II)]}(base-off) is further reduced to obtain H2O-Cbl[Co(I)]. (C) 1997 Elsevier Science S.A.

Electrochemical studies on vitamin B-12 and its derivatives

The electrochemical studies on vitamin B-12 and its derivatives were reviewed in this paper. The importance of electrochemical studies for explaining the mechanism of B-12 coenzyme in body was discussed. The latest results of electrochemical studies on vitamin B-12 and its derivatives was reviewed. A prospect for the electrochemical studies in vitamin B-12 and its derivatives was suggested.

Regulation of autoinducer 2 production and luxS expression in a pathogenic Edwardsiella tarda strain

Edwardsiella tarda is a bacterial pathogen that can infect both humans and animals. TX1, an Ed. tarda strain isolated from diseased fish, was found to produce autoinducer 2 (Al-2)-like activity that was growth phase dependent and modulated by growth conditions. The gene coding for the Al-2 synthase was cloned from TX1 and designated luxS(Et). LuxS(Et) was able to complement the Al-2 mutant phenotype of Escherichia coli strain DH5 alpha. Expression Of luxS(Et) correlated with Al-2 activity and was increased by glucose and decreased by elevated temperature. The effect of glucose was shown to be mediated through the cAMP-CRP complex, which repressed luxS(Et) expression. Overexpression of luxS(Et) enhanced Al-2 activity in TX1, whereas disruption of luxS(Et) expression by antisense RNA interference (i) reduced the level of Al-2 activity, (ii) impaired bacterial growth under various conditions, (iii) weakened the expression of genes associated with the type III secretion system and biofilm formation, and (iv) attenuated bacterial virulence. Addition of exogenous Al-2 was able to complement the deficiencies in the expression of TTSS genes and biofilm production but failed to rescue the growth defects. Our results (i) demonstrated that the Al-2 activity in TX1 is controlled at least in part at the level of luxS(Et) expression, which in turn is regulated by growth conditions, and that the temporal expression of luxS(Et) is essential for optimal bacterial infection and survival; and (ii) suggested the existence in Ed. tarda of a LuxS/Al-2-mediated signal transduction pathway that regulates the production of virulence-associated elements.

Regulation of autoinducer 2 production and luxS expression in a pathogenic Edwardsiella tarda strain

Edwardsiella tarda is a bacterial pathogen that can infect both humans and animals. TX1, an Ed. tarda strain isolated from diseased fish, was found to produce autoinducer 2 (Al-2)-like activity that was growth phase dependent and modulated by growth conditions. The gene coding for the Al-2 synthase was cloned from TX1 and designated luxS(Et). LuxS(Et) was able to complement the Al-2 mutant phenotype of Escherichia coli strain DH5 alpha. Expression Of luxS(Et) correlated with Al-2 activity and was increased by glucose and decreased by elevated temperature. The effect of glucose was shown to be mediated through the cAMP-CRP complex, which repressed luxS(Et) expression. Overexpression of luxS(Et) enhanced Al-2 activity in TX1, whereas disruption of luxS(Et) expression by antisense RNA interference (i) reduced the level of Al-2 activity, (ii) impaired bacterial growth under various conditions, (iii) weakened the expression of genes associated with the type III secretion system and biofilm formation, and (iv) attenuated bacterial virulence. Addition of exogenous Al-2 was able to complement the deficiencies in the expression of TTSS genes and biofilm production but failed to rescue the growth defects. Our results (i) demonstrated that the Al-2 activity in TX1 is controlled at least in part at the level of luxS(Et) expression, which in turn is regulated by growth conditions, and that the temporal expression of luxS(Et) is essential for optimal bacterial infection and survival; and (ii) suggested the existence in Ed. tarda of a LuxS/Al-2-mediated signal transduction pathway that regulates the production of virulence-associated elements.